1. Field
The present disclosure relates generally to communication and more specifically to techniques for controlling transmission power of a first message of a physical uplink shared channel (PUSCH) during a random access channel (RACH) procedure.
2. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) represents a major advance in cellular technology and is the next step forward in cellular services as a natural evolution of Global System for Mobile communications (GSM) and Universal Mobile Telecommunications System (UMTS). LTE provides for an uplink speed of up to 75 megabits per second (Mbps) and a downlink speed of up to 300 Mbps and brings many technical benefits to cellular networks. LTE is designed to meet carrier needs for high-speed data and media transport as well as high-capacity voice support well into the next decade. Bandwidth is scalable from 1.25 MHz to 20 MHz. This suits the needs of different network operators that have different bandwidth allocations, and also allows operators to provide different services based on spectrum availability. LTE is also expected to improve spectral efficiency of 3G networks, allowing carriers to provide more data and voice services over a given bandwidth. LTE encompasses high-speed data, multimedia unicast and multimedia broadcast services.
The LTE physical layer (PHY) is a highly efficient means of conveying both data and control information between an enhanced base station (eNodeB) and mobile user equipment (UE). The LTE PHY employs some advanced technologies. These include Orthogonal Frequency Division Multiple Access (OFDMA) and Multiple Input Multiple Output (MIMO) data transmission on the downlink (DL) and Single Carrier-Frequency Division Multiple Access (SC-FDMA) on the uplink (UL). OFDMA and SC-FDMA allow data to be directed to or from multiple users on a set of subcarriers basis denoted by resource block (RB) for a specified number of symbol periods.
The Medium Access Control (MAC) layer is above the physical layer and performs uplink functions that include random access channel, scheduling, building headers, etc. Transport channels at the MAC layer are mapped onto PHY layer channels. The Uplink Shared Channel (UL-SCH) is the primary transport channel for data transmission on the UL and is mapped onto the Physical Uplink Shared Channel (PUSCH). Format variables are resource assignment size, modulation and coding, which determine data rate. When the UE is not connected or is not synchronized, no transmit subframes are scheduled. The Random Access Channel (RACH) provides a means for disconnected or not synchronized devices to access the UL. Transmitting on the PUSCH requires a resource allocation from the eNodeB, and time alignment to be current. Otherwise the RACH procedure is used.
The RACH procedure is used in four cases: initial access from a disconnected state (RRC_IDLE) or radio failure; handover requiring a random access procedure; downlink (DL) data arrival during RRC_CONNECTED after UL PHY has lost synchronization (possibly due to power savings operation); or UL data arrival when there is no dedicated scheduling request (SR) on PUCCH channels available. There are two forms for RACH transmission: Contention-based, which can apply to all four events above, and noncontention based, which applies to only handover and DL data arrival. The difference is whether or not there is a possibility for failure using an overlapping RACH preamble.